Tuesday’s sentencing of Nizar Zakka – a Lebanese citizen who lives in Washington, advocates for internet freedom and whose non-profit group did work for the US government – came as Iranian officials travelled to the UN general assembly this week in New York.

It also highlighted the challenge faced by western governments and those wanting closer ties with Iran, where hardliners in the country’s security forces target dual nationals and others, using secret trials.

“There’s no regard for any international order, any international agreement or any international state of relations that they care about,” said David Ramadan, a former Virginia state legislator who co-founded the Friends of Nizar Zakka group.

Jason Poblete, a US lawyer representing Zakka, said in a statement that a revolutionary court in Tehran had handed down the sentence in a 60-page verdict which Zakka’s supporters have yet to see.

Amnesty International has said Zakka had only two court hearings before the ruling and received only limited legal assistance before appearing at the revolutionary court, a closed-door tribunal that handles cases involving alleged attempts to overthrow the government.

Supporters say Judge Abolghassem Salavati heard Zakka’s case. Salavati is known for his tough sentences and has heard other politically charged cases, including one in which he sentenced the Washington Post journalist Jason Rezaian to prison. Aprisoner swap in January between Iran and the US freed Rezaian and three other Iranian-Americans.

There was no mention of Zakka’s sentence in Iranian state media. Iran’s UN mission did not respond to a request for comment.

Zakka, who holds resident status in the US, leads the Arab ICT Organisation, or IJMA3, an industry consortium from 13 countries that promotes information technology in the region. Zakka disappeared on 18 September 2015 during his fifth trip to Iran. He had been invited to attend a conference at which President Hassan Rouhani spoke of providing more economic opportunities for women and sustainable development.

On 3 November, Iranian state television reported he was in custody and called him a spy with “deep links” to US intelligence. It also showed what it described as a damning photo of Zakka and three other men in army-style uniforms, two with flags and two with rifles on their shoulders. It turned out to be from a homecoming event at Zakka’s prep school, the Riverside military academy in Georgia, according to the school’s president.

It is unclear what prompted Iranian authorities to detain Zakka. The Associated Press reported in May that IJMA3 had received at least $730,000 in contracts and grants since 2009 from both the US state department and USAid, the government agency responsible for foreign aid and development.

Zakka’s supporters have written to the US secretary of state, John Kerry, stating that he travelled to Iran “with the knowledge and approval of the US state department, and his trip was funded by grants” from it. Those assertions could not be verified by the AP and Zakka’s friends said they could not obtain copies of the contract from the state department due to federal regulations.

Neither US nor Lebanese officials, who the US says are responsible for providing consular assistance to Zakka, have publicly acknowledged his work with the US government. The state department did not immediately respond to a request for comment, but Ramadan said he still held them responsible for Zakka’s safety.

“The US state department refuses to do anything for him,” he said.

Others known to have been detained in Iran since the nuclear deal include:

Homa Hoodfar, an Iranian-Canadian woman who is a retired professor at Montreal’s Concordia University.

Siamak Namazi, an Iranian-American businessman who has campaigned for closer ties between the two countries and whose father is also held in Tehran.

Baquer Namazi, a former Iranian and UN official in his 80s who is Siamak’s father.

Robin Shahini, an Iranian-American detained while visiting family who had previously made online comments criticising Iran’s human rights record.

And Nazanin Zaghari-Ratcliffe, a British-Iranian woman sentenced to five years in prison on allegations of planning the “soft toppling” of Iran’s government while travelling with her young daughter.